translator: add translator_ld{ub,sw,uw,l,q}

We don't bother with replicating the fast path (tlb_hit) of the old
cpu_ldst helpers as it has no measurable effect on performance. This
probably indicates we should consider flattening the whole set of
helpers but that is out of scope for this change.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Emilio G. Cota <cota@braap.org>
[AJB: directly plumb into softmmu/user helpers]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>